| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 2000: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
High efficiency blue LEDs and ultra-violet LD have been commercialized and realized with devices fabricated from the stable hexagonal GaN (a-GaN)/sapphire system. Metastable cubic GaN (b-GaN) is expected to have many advantages in physical properties over those of the hexagonal phase including lower resistivity and higher doping efficiency due higher crystallographic symmetry. Cubic GaN can be grown on GaAs, and the possibility of using GaAs substrates is one of the important advantages for device fabrication due to its ability to be easily cleaved. We have demonstrated highly pure cubic-GaN epilayer growth using an AlGaAs buffer layer grown on GaAs (100) by molecular beam epitaxy. ^<(1)> In that work, it was concluded that the window of optimal growth condition in order to achieve high phase purity is very narrow, and there was one problem that the layer thickness of epilayer is only 0.4 mm. In this work, detailed investigation of the initial growth condition which influence to phase
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purity of the epilayer, and the dependence of layer thickness on the crystallinity were carried out.
Plasma-assisted molecular beam epitaxy was used for film growth using Si doped n-type GaAs (100). Details of the growth procedure have been described elsewhere. ^<(2)> Figure 1 shows a three dimensional X-ray reciprocal space map in the vicinity of the cubic-GaN (002) reflection of the epilayer on a nitrided Al_<0.1>-Ga_<0.83>As buffer layer. The thickness of the epilayer is 0.4 mm. We could not detect any peak attributed to the hexagonal crystal by detailed X-ray pole figure measurement. These results indicate that the epilayer is the cubic (002) phase without any hexagonal phase. It was observed that the surface condition of the AlGaAs bufer layer influences the phase purity of the epilayer. Figure 2 shows that the surface, which was observed (4x1) reconstruction RHEED pattern (probably due to an As stabilized surface, leads to a high phase purity of the epilayer, while the surface, which was observed a (1x1) RHEED pattern. leads to the mixing with the hexagonal phase at early growth stages. Detailed investigations are now underway. Figure 3 shows the result of X-ray pole figure measurements for an epilayer, which was observed (1x1) RHEED pattern after AlGaAs buffer layer. Four peaks attributed to hexagonal crystals, which were grown on four equivalent (111) facets of cubic crystal structure, were detected around y=54゜. These results suggest that the As stabilized surface of an AlGaAs buffer layer suppresses the growth of the hexagonal crystal. Less
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